It's really hard to know who you can and can't trust with these kind of things, especially irl where telling the wrong person can lead to a lot of problems not just in general between you and others, but also problems for going through with your plans if you decided you want to. I prefer to keep it to myself because I know everyone I know irl would make it almost impossible for me to go through with it, but there seem to be people who do find someone to trust. I guess my general advice is to make sure you know what kind of person they are, what they believe about choices and so on, before inching your way into the subject. And maybe don't go into details, unless you're sure they can take it and won't share further?